feat(gen): handle predicate aliases

handle cases where a predicate is defined as an alias, i.e. without any parameters

midas/checker/midas.py

@@ -167,6 +167,7 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
             Predicate(
                 type=type,
                 body=stmt.body,
+                alias=len(params) == 0,
             ),
         )
 

midas/checker/types.py

@@ -242,6 +242,7 @@ def unfold_type(type: Type) -> Type:
 class Predicate:
     type: Type
     body: m.Expr
+    alias: bool
 
 
 Type = (

midas/generator/constraints.py

@@ -63,7 +63,7 @@ class ConstraintGenerator(m.Expr.Visitor[ast.expr]):
                 )
                 alias: str = self.make_alias(None)
                 definition: ast.stmt = self.make_definition(
-                    alias, Predicate(type=func, body=expr)
+                    alias, Predicate(type=func, body=expr, alias=False)
                 )
                 self._definitions.append(definition)
                 return ast.Name(id=alias)
@@ -79,8 +79,15 @@ class ConstraintGenerator(m.Expr.Visitor[ast.expr]):
         return alias
 
     def make_definition(self, name: str, predicate: Predicate) -> ast.stmt:
-        body: list[ast.stmt] = [ast.Return(value=predicate.body.accept(self))]
-        return self.make_func(name, body, predicate.type)
+        body: ast.expr = predicate.body.accept(self)
+        if predicate.alias:
+            return ast.Assign(
+                targets=[
+                    ast.Name(id=name),
+                ],
+                value=body,
+            )
+        return self.make_func(name, [ast.Return(value=body)], predicate.type)
 
     def make_args(self, func: Function) -> ast.arguments:
         return ast.arguments(
@@ -116,7 +123,7 @@ class ConstraintGenerator(m.Expr.Visitor[ast.expr]):
                 )
 
             case _:
-                raise ValueError(f"Expected function, got {type}")
+                raise ValueError(f"Expected function, got {type!r}")
 
     def get_predicate(self, name: str) -> Optional[ast.expr]:
         if name not in self._aliases: